Mercury arc rectifier



Dec. 6, 1949 J. c. READ MERCURY ARC RECTIFIER Filed Jan. 9, 1945Inventor John Carleg Read,

by W

'His Attorney.

Patented Dec. 6, 1949 John Carley Read, :Inwoods, Rugby, England, as-

signor to General Electric Company, a corpo ration of New YorkApplication January 9, 1945', s mi so. 571,978 In Great Iiritain January14, 1944 2 was. (o1. ass-27.5)

This invention relates to mercury arc rectiflers lower, side oi thebaiile or grid. These ions which and the like, and more particularly toa method i of reducing the tendency to backflres, especially at highvoltages.

It is generally considered that a contributory cause of such backflresis the bombardment of the anode by positive ions which occurs during thetime when the anode is negative. the higher voltages a considerable part"of this positive ion bombardment is produced by positive ions attractedinto the anode from beyond the de-ionising baflle or grid. It is theobject of the invention to reduce the effectiveness for initiatingbackfires of the bombardment produced by these positive ions.

According to one form of the invention 1 reduce the quantity of positiveions that are able In rectifiers for to be attracted to the anode fromthe iar side of the grid, by certain arrangements of multiple grids withsuitable potentials applied tothem. In another form I cause thisbombardment to be less continuously concentrated on the same part of theanode surface. In another form I cause this bombardment to fall on partsof the' 'anode" surface where the electrostatic field strength is low.In another form I divide theanode into a main part which does notreceive the bombardment and an auxiliary part, connected to the mainpart through a suitable high impedance, so arranged thatthis'bombardment fallson the auxiliary part of the anode.

The invention will be better understood by ref erence to theaccompanying drawings, in which Figures 1 to 6 represent various formsoi the invention. In the drawings corresponding parts 1 all cases.

Referring to Fig. 1, l represents an anode of a V high-voltage mercuryarc rectifier or'thelike,"

to enable a control potential to be applied to it.-

During the time when the anoderis-negative a;

considerable part of the positive 191 bombardmentiwhich it is subjectedto is producedby ions are designated by thesame reference numerals in 3attracted to the anode from the further, i. ate;-

reach the anode from the further side of the grid are not distributedover the'surface of the anode, but their bombardment is concentrated onparticular points 6 which are respectively about opposite the centres ofthe holes 8 in the grid, the ions falling on these spots along pathsrepresented by the dotted lines' l. The intensity of bombardment at thepoints 8 greatly exceeds that .over' the remainder of theanode surface.

According to one form of the invention I may reduce the averageintensity of bombardment on these spots by rotating the anode or grid ontheir own axes; and the various holes in the grid may be so located thatthe tracks of the centres of different holes which are thus traced outon the anode face do not coincide. Alternatively the spots 8 where thelocal bombardment takes place from each of the grid holes may be causedto rotate or oscillate by applying a tranverse magnetic field, forexample as indicated by the coils shown dotted at M. In either case thebombardment is thus spread over arelatively large area of the anodeface. I

Another form of the invention is shown in Fig. 2, in which two grids 4and 9 respectively, are provided one above the other and fairly closelyspaced apart. In using this arrangement the control potentials appliedito the two grids are maintained such that, at least during the timewhen the anode is negative with respect to the cathode, the nearer grid4 is positive with respect to the farther grid 9. The. potentialdifierence between grids 4 and 9, the spacing between them, and the sizeof holes are so-chosen that the electrostatic field in the spacebetween4 and '9' due entering one of the holes in 9 will first experience arepelling field due to the potential on 4 and thus the" anode is unableto attract to itself positive ions iron: the space below the lower grid9. Conveniently this potential' hetwfeen 4 and 9 may be applied byapplying to -both 4 and 9 identically similar A. C. voltagessuperimposed on different D, C. bias voltages, in the manner commonlyunderstood. In this way, providing the dimensions and grid potentialdifference are suitable as described above; the concentrated bombardmentof the anode bypositive ions irom the far side of the grids can bepractically-eliminated.

Fig. 3 shows another; in which; again two grids?! and 9, are employed,

with different potentials on' them. In this case, J

orm oi the invention,

however, during the time when the anode is negative the upper grid 4is'allowed to be negative with respect to the lower grid 9, either byhaving such a potential applied to it by external means, or by acquirinthis potential by virtue 5 of its capacity to the negatively chargedanode, the upper grid 4 in thisf'lfittGFCB-Sltbd-DEBBMIY. or completelyinsulated. In this formof the invention, however, the passages 8 throughthe upper grid 4 are made of tortuous form so that: a particle can onlypass through 8 by following a...

4 H to depart far from that of I, but at the same time the presence ofthe high impedance in series with H prevents the establishment of abackthe on l4 as a result of the ion bombardment to which this issubjected.

Further, similar results can be obtained with simpleranodeconstructionthan that in Fig. 5. Ingeneral any form 01" anode may be employed wherethe anode is similarly divided into a main m part which carries thenormal power current and .anfllauxiliary part connected to the main partsharply curved path. The actual form'of the" tortuous passages throughLia mother. realest;

not relevant to this present: invention, :hut. for

through 4 is made too sharp for a. particle a-1-- ready possessing this:velocity to be-abIe to get. round thecorners without: striking some:part of, the grid. 4; Thus again few or none of the noeltive ionsentering. from below the lower able'to bombard the-anode. I

It has already been explained inconneetiolrwith. Fig. 1- that the. ints6- on theanodeface: where the intense bombardment occurs are verysmalland exactly located- According to-an'other form of the invention, shownin Fig.4. small 1 holes or grooves I3 are provided in the anode;- faceexactly located. where-theserpoints of; intense bombardment occur. Thevelocityof theionby the time that it approaches the anode'face. is'sohigh that it travels almost in a straight line,. and consequently thebombardingparticles then strike; the anode down inside these holes orgrooves... The bombarding particles therefore: impinge on: a pointwherethe electrostaticfieldstrengthzis through a high impedance asdescribed, providing; thatthe main: and auxiliary parts of the anode.which; should preferably be closely adjacnfitoone another, are solocated relative to the holes in. the. adjacent de-ionislng baflle or,gridi' thatisuclr bombarding positive ions enteringj through the latterwill fall on the auxiliary Withi this" part: of: the anode. Forpractical purposes this means that all the electrostatic stress linesfrom the grid. holes tothe anode will fall on the auxiliarypartotitheanode;

-Manyconstructions that would comply with these requirements will beobvious to those skilled in-the art. An example of such a constructionis shownin Fig. 6..

.In' Fig. 6 the anodeis thus divided into an annular main-part. l whichcarries the normal power current and is connected through its tubularsupport: stem 2 tov the connection l5 leading to the main transformer;and an auxiliary part H of die -like: form closely adjacent. to the mainpart l,.- and connected through its steml6 and the external highimpedance 11 to- I. The main part of .the anode is supported andinsulated from the vacuum chamber l8 of-the rectifier by aleadin.;insulator l9 of any of the known forms; and the auxiliary anodeis inturn insulated from this by a -further lead-in insulator 2. Thegrid 4 which is mounted on its support insulator 5 par--- tiallysurrounds' themain and auxiliary parts of the anode, and during the timewhenthe anode is. negative the electrostatic stress lines conse-.

quently take: the form. approximately sketched by the dotted lines 2|.The location of theauxmuch lower than on the: outer surface of the rs'pan of amde with respect to the anode; and furthen'the materialsputtered out. of the anode by the bombardment tendslargely to beretained inside the holes orgrooves. The

positive ion bombardmentis in. this.- case: lessei- 5 fectlve inproducing backfires. I

Alternatively, as shown iII'Fig;' 5; the anode: may actually be madehollow with theholes on grooves I3 passing right throughttrthe'interion. If the hollow space inside the; anode is left. emptythe ions will then bombard ztheinterior surface of: the anode; where:the-field strength is; zero;

In a further form. of the inventiom-horvevem" anadditional electrodeorauxiliary anode; shown dotted at M- in. Fig. 5- may be provided insidethe:

hollow anode, so placed that if it is: at or about the same potential.as the main ano'de "l: the ions passing in through the holes 13' alongpassagx as indicated by the dotted'lines i "will be. col-er. lected onthis auxiliary anode.. 'The actual rent. flow corresponding to thisflow/oi. bomBlmting ions is very small. I therefore connectthe:auxiliary anode H to the-main anode I through a very high impedance;which may be either internal 01' external tothe rectifier, thishigh im--holes. 8 in. the grid. is such that thestress lines from theseholestothe anode-all fall on the auxiliary partof the: anode, and thusbombarding. positive ionsentering from outside the grid will.

0- impinge on the auxiliary part ofthe anode,

5550f values. as already describedin connection with Fig. 5.

Alternatively thehigh impedance can take'the form. of. a1semi-conducting rod forming" part of the-length of the auxiliary anodestem l6, i. 6:. inside the rectifier: In this casev the additionallead-in-insulator 20 is not required. If the impedance is thus internalit should preferably be weli' screened-from the generalionisation' ofthe arc; as would in'fact 'bethe case with a construction on the lines:illustrated in Fig. 6.

Arrangements such as shown in Fig. S'may be used in conjunction with anyof the arrangementsin Figs. 1 to 52 For example, the auxiliary part M ofthe anode may have holes or' grooves pedance taking the form of: a high.resistance or 7 provided inits bottom face at the points where currentthis current. is. ableto pass throughthehigh. impedancewithoutcausing-the potential at the bombardingpositive ions strike it,as in Fig. i. 'I'lie'Jcharacter'istic featureof constructions accordingto theinvent'ion, in which the anode ls' divided into two parts thusthat'theload as; exemplified in Fig. 6, is

current is carried on one part while the other part, which is incapableof sustaining a backfire, receives the positive ion bombardment, byutilising the fact that the bombarding positive ions entering throughthe grid holes travel in nearly straight lines, whereas the normal flowof load current can follow a relatively curved path and thus can flowfrom the grid holes to the main part of the anode.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In discharge apparatus of the type in which the discharge takes placebetween an anode and a cathode through an ionizable medium, thecombination which comprises an anode having a discharge receivingsurface, an electrode interposed between said surface and the cathode ofthe apparatus, said electrode having a plurality of openings positionedtransversely of the discharge path for sub-dividing the forwarddischarge, and means producing an electromagnetic field in the regionbetween said discharge receiving surface and said electrode for causingrelative motion between the discharge receiving surface of the anode andthe sub-divided forward discharge to spread the discharge over anextended portion of the discharge receiving surface.

2. In discharge apparatus of the type in which the discharge takes placebetween an anode and a cathode through an ionizable medium, thecombination which comprises an anode having a discharge receivingsurface, an electrode interposed between said surface and the cathode ofthe apparatus, said electrode having a plurality of openings positionedtransversely of the discharge 6 path for sub-dividing the forwarddischarge, and means producing relative motion between the dischargereceiving surface of the anode and the sub-divided forward discharge tospread the discharge over an extended portion of the discharge receivingsurface.

JOHN CARLEY READ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 841,386 De Forest Jan. 15, 19071,066,505 Kraus et a1. July 8, 1913 2,097,490 Kobel Nov. 2, 19372,116,393 Griffith May 3, 1938 2,148,300 Krines Feb. 21, 1939 2,320,685Von Bertele June 1, 1943 FOREIGN PATENTS Number Country Date 339,022Great Britain Dec. 4, 1980 341,578 Great Britain Jan. 22, 1931 395,383Great Britain July 6, 1933 422,870 Great Britain Jan. 21, 1935 425,896Great Britain Mar. 25, 1935 430,915 Great Britain June 27, 1935 432,434Great Britain July 26, 1935- 448,545 Great Britain June 10, 1936 458,777Great Britain Dec. 28, 1936 493,534 Great Britain Jan. 4, 1937

